In one embodiment, a method includes accessing a data store comprising a log of requests transmitted by a plurality of remote hosts, each request corresponding to one or more resources maintained by a web site; analyzing the requests and one or more attributes of the resources corresponding to the respective requests using a cost function relating to network performance, wherein a first component of the cost function is directed to a performance improvement achieved by grouping one or more of the resources for transmission to one or more remote hosts and a second component is directed to a performance inefficiency caused by grouping the one or more resources for transmission to the one or more remote hosts; and identifying one or more groupings of one or more resources that optimize the cost function for network performance.